I have been updating the ghc-exactprint library for real world use cases on
the about to be released GHC 9.2.1, and realised I need to be able to put
an Anchor into every SrcSpan in the ParsedSource AST.
I prepared !6854 to sort it out in master and turned to the problem of GHC
9.2.1, where I had missed the boat.
And then I discovered that we have SrcSpan defined as
data SrcSpan =
RealSrcSpan !RealSrcSpan !(Maybe BufSpan)
| UnhelpfulSpan !UnhelpfulSpanReason
and the (Maybe BufSpan) is only used for attaching haddock comments after
parsing.
This means there is an isomorphism between the RealSrcSpan variant and an
Anchor, which I take advantage of with the code in [1], by using the Maybe
to encode the AnchorOperation and the BufSpan to encode the DeltaPos.
And it struck me that perhaps we should make this a more official
approach. The only problem is the detail of the BufSpan, to be able to
play both roles cleanly.
Alan
[1] https://gist.github.com/alanz/5e262599ab79138606cdfcf3792ef635
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